The invention relates to a force-responsive longitudinally extending sensor, comprising first longitudinally extending electrically conductive means, second electrically conductive means superimposed on the first means, electrically insulating means positioned between and spacing the first means from longitudinally distributed parts of the second means, respective remaining parts of the second means being longitudinally distributed along the sensor and normally being resiliently held spaced apart from the first means but each being able to be flexed independently of the other remaining parts and against the resilience into contact with the first means in response to a force applied to that remaining part whereby to enable a force-responsive output to be produced, and means defining protruding means extending transversely to the longitudinal extension of the sensor and outwardly of the second means in a direction away from the first means for receiving a force and transmitting it to the remaining parts.
Such a sensor is shown, for example, in DE-A-197 06 481. In this sensor, the second electrically conductive means is of ladder-like configuration with parallel side pieces extending along the length of the sensor and electrically insulated by insulating means from the first electrically conductive means. The cross pieces of the ladder-like configuration of the second electrically conductive means extend resiliently across gaps in the electrically insulating means so that they can be pressed into respective electrical contact with the first electrically conductive means in response to a force applied to anyone or more of them individually.
However, if a force is applied over an area encompassing the side pieces and a plurality of the cross pieces of the ladder-like configuration of the second electrically conductive means, the necessary force applied individually to one.of the cross pieces, for flexing it into contact with the first electrically conductive means, may not be produced. Therefore, the sensor may not produce any output in response to the force. The invention aims to deal with this problem.
Such a sensor as first set forth above is also known from U.S. Pat. No. 4,621,223. This document shows a sensor in which parallel side by side first and second electrically conductive layers are formed on the same surface of an electrically insulating sheet which is folded over to present the conductive layers to each other with a longitudinally extending electrical insulator of ladder-like configuration between them. An externally applied force can flex part of the first conductive layer into contact with the second conductive layer through one of the gaps in the insulator. However, if such a force is applied over a relatively large area, it may not be able to produce such contact because the cross pieces of the ladder-like configuration of the insulator will prevent the necessary flexing of the first conductive layer.
According to the invention, therefore, the sensor as first set forth above is characterised in that the or each protruding means is positioned in alignment with a respective one, only, of the remaining parts for receiving a force applied over an area encompassing a plurality of the remaining parts and transmitting that force to that one of the remaining parts.